1. Field of the Invention
The present invention relates to a display control apparatus, and more particularly, to a display control apparatus and a method thereof which allows easy control of a display apparatus and a small size of memory used in displaying images on a display screen.
2. Description of the Related Art
In a display screen of a computer or a game machine, moving objects such as a fighter aircraft, a player and a ball which move on the display screen are overlapped on the background. In that case, usually, memory for the background images and memory for the moving objects are installed separately in the computer or the game machine, and the moving objects are moved on the display screen by changing a display position of the moving objects. The technique is generally referred to as a sprite controlling technique by those who are skilled in the art.
FIG. 1 shows a construction of V-RAM 202 in the sprite controlling technique disclosed in Japanese Kokai publication No. HEI 6-83320. Character patterns for a background image are stored in a character storing part 206. In this example, one character consists of a total of 64 dots, that is 8 dots in vertical direction and 8 dots in horizontal direction. Also, a character code is provided to each of the character patterns.
On the other hand, the display screen is divided into a plurality of regions each of which corresponds to the size of a character as shown in FIG. 2. In this example, the display screen is divided into a plurality of regions of 32 (in vertical direction) times 32 (in horizontal direction), and the divided regions are numbered with 0 to 3 FF respectively. A plurality of storing regions each of which corresponds to each of the regions as described above are provided in a background instruction part 204 shown in FIG. 1, and different character codes of desired characters are specified in the storing regions (see FIG. 3). Display data are generated by a controlling circuit (not shown) based on the stored information in the character storing part 206 and the background instruction part 204. Thus, a background image is displayed on the display screen.
Character pattern and character codes for sprite are stored in a character storing part 210 shown in FIG. 1. The data shown in FIG. 4 are stored in a sprite instruction part 208, that is, X coordinate, Y coordinate on the display screen of a desired character, and a desired character code are specified. The controlling circuit (not shown) displays a sprite based on the stored information in the character storing part 210 and the sprite instruction part 208. Also, display of the sprite can be moved by changing the X coordinate and Y coordinate of the desired character (see FIG. 4).
The data structure shown in FIG. 3 and FIG. 4 is simplified for easy explanation. Color data and display priority or the like are included in addition to the data.
However, there are the following disadvantages in a display controlling apparatus in the related art described hereinbefore.
Firstly, since the display of the background image is almost inflexible, it is not easy to move the background images smoothly on the display screen. A huge number of different images have to be stored in memory when a smooth movement of the background is required.
Secondly, different control circuits are required for controlling the background images and for controlling of the sprite. Therefore, the structure of the apparatus is complex. Also, complicated computer software is required to control the background images.
Meanwhile, there is a case to display a spherical object such as the earth or the like in rotation. In that case, a plurality of slightly different display image patterns each of which shows the spherical object rotated in different phases are prepared, and then the rotating spherical object is displayed on a CRT (display screen)by successively changing the display image patterns using computer software. Thus, it is possible to display the spherical object in rotation for a game player or for a person watching the display screen.
However, it is required to have a huge number of display image patterns to be changed in a given period of time in order to display the spherical object being rotated smoothly using a predecessor computer game machine. Accordingly, the size of the memory storing the display image patterns must be large. In addition, CPU is overloaded to execute the above-mentioned display. In the worst case, other jobs are suspended during the execution of the above display. On occurrence of such situation, a game player cannot play a game and is irritated by that situation due to the suspension.
To resolve the above-described problems, it is considered to use a powerful CPU or an extension processor. Although this approach can simply avoid the suspension of game programs, production cost of the computer game machine is increased. Moreover, even the above approach still requires a large size of memory.